I've just realised that music from 5.1 cinematics:
Is the same music that was used in Warcraft III Cinematic (play the video from 1:55 to hear it):
"As mortal armies rush blindly towards their doom, the burning shadows comes to consume us all."
And that's what Horde and Alliance is doing in 5.1 and in whole Mists of Pandaria expansion. Is this another hint telling us that the next expansion will be about Burning Legion?